Method articles and compositions of matter containing large capsules

ABSTRACT

THIS DISCLOSURE IS DIRECTED TO A METHOD FOR FORMING ARTICLES CONTAINING LARGE (500 TO 5000 MICRONS) CAPSULES IN A FLEXIBLE MATRIX BY DEPOSITING LARGE CAPSULES UPON VARIOUS SUPPORT SUBSTRATES WHILE MINIMIZING PREMATURE CAPSULES CELL WALL RUPTURE AT THE TIME OF DEPOSITION AND PRIOR TO USE; ARTICLES OF MANUFACTURE CONTAINING THESE LARGE CAPSULES AND THIXOTROPIC COMPOSITIONS USED TO PREPARE SUCH ARTICLES. THE FORMING PROCESS EMPLOYS A THIXOTROPIC AQUEOUS MATRIX CONTAINING AN ORGANIC POLYMER GEL-FORMING, A FLEXIBLE BINDER (USUALLY A READILY WATER-SOLUBLE OR WATERDISPERSIBLE ELASTOMERIC BINDER) AND VARIOUS OPTIONAL ADJUVANT FILLERS. ACCORDING TO A PREFERRED EMBODIMENT, THE THIXOTROPIC GEL CONTAINING THE LARGE CAPSULES IS EXTRUDED ONTO A FLEXIBLE SUBSTRATE SUPPORT FOLLOWED BY DRYING.

METHOD, ARTICLES AND COMPOSITIONS OF MATTER CONTAINING LARGE CAPSULES;

Theodore Maierson, Dayton, Ohio, assignor to The National Cash Register Company, Dayton, Ohio N Drawing. Filed Apr. 1, 1969, Ser. No. 812,440 lint. Cl. A471 23/05; B011) 13/02; 1808b 1/00 US. Cl. 15104.93 19 Claims ABSTRACT OF THE DISCLOSURE This disclosure is directed to a method for forming articles containing large (500 to 5000 microns) capsules in a flexible matrix by depositing large capsules upon various support substrates while minimizing premature capsule cell wall rupture at the time of deposition and prior to use; articles of manufacture containing these large capsules and thixotropic compositions used to prepare such articles. The forming process employs a thixotropic aqueous matrix containing an organic polymer gel-former, a flexible binder (usually a readily water-soluble or waterdispersible elastomeric binder) and various optional adjuvant fillers. According to a preferred embodiment, the thixotropic gel containing the large capsules is extruded onto a flexible substrate support followed by drying.

At present there is a need to provide various encapsulated materials in the form of large sized capsules suitable for applicator use, e.g., containing such convenience internal phase compositions as shoe polish, fragrances, cosmetic lotions, creams, etc. Great difiiculty has been experienced in forming capsular products containing large capsules in that it is difficult to apply such large capsules onto flexible supports. Moreover, extensive rupture of the capsule walls has occurred prematurely in the deposition of the capsules by conventional coating techniques by the use of bar coater, roll coater, air knives, spray coating procedures and modified printing methods such as flexographic and gravure coating procedures. Thus, it is apparent that the readily available coating procedures are not suited for the application of large capsules to substrates. It is this need which lead to the development of the procedure, articles and compositions of this invention.

This invention is directed to a method of forming capsular products having large capsules, viz, capsules having diameters ranging from about 400 to about 5000 microns, in a thixotropic polymeric matrix having components which are water-soluble or readily water-dispersible. The capsule-containing matrix is located on a supporting member which can contain a single layer or multi-layer composite. Preferably, the support is flexible, e.g., paper, plastic sheets, etc. The forming method comprises establishing a thixotropic gel comprised of a hydrophilic water-soluble or Water-dispersible gel-forming organic polymer, water, usually a flexible binder, e.g., natural and synthetic water-soluble or water-dispersible elastomers (optional), a plurality of and usually a profusion of large capsules containing any desired solids, liquids, mixtures of liquids and solids internal phase, and optional adjuvant fillers; depositing the thixotropic mix containing the large capsules onto said support substrate in a controlled thickness, e.g., by extrusion, at a viscosity of from about 1000 to about 10,000 centipoises; and drying the thus established thixotropic mix to evaporate therefrom extraneous liquids. This invention offers a processing advantage in that use of the thixotropic compositions as taught herein enables the capsule-containing matrix to be extruded onto the supporting substrate to substantially the desired thickness sought in the end product. Some shrinkage can occur in drying.

United States Patent O m 3,619,842 Patented Nov. 16, 1971 SUPPORT MEMBER While a plurality of upper and lower support members of the same or dissimilar materials can be employed, e.g., to form a sandwich structure with the capsule-containing matrix in the central portion thereof; the articles produced in accordance with this invention can utilize a single support member usually of a flexible material. Suitable candidate support substrate materials include but are not limited to the following: paper, and flexible materials comprised of paper including paper toweling and various papers having varying contents of natural and synthetics fibers; foamed plastic sheets including open celled poly (vinyl chloride), foamed rubber, and polystyrene sheets; plastic films and sheets, including various natural and synthetic rubbers, resins, polyolefins, polyethylene, polypropylene, ethylene-propylene copolymers (cellophane, poly(vinylidene chloride), e.g., saran, poly carbonates, e.g. Lexan, polyesters such as Mylar, Viz, polyethylene glycol terephthalate), polyurethane sheets and films, etc.; various natural and synthetic woven and non-woven fabrics which can be organic, inorganic and mixtures of natural and/or organic and/or inorganic fibers, e.g., cotton, rayon, nylon, Dacron (polyethylene glycol terephthalate); Orlon (polyacrylonitrile fiber); metal foils, e.g., aluminum foil, tinfoil, steel foil, gold foil, silver foil, copper foil, etc.; composite supports which have two or more of the above components laminated or otherwise secured together, e.g., paper backed with plastic in the form of barrier films, sheets or coatings secured to the paper; plastic-fabric composites, including composites wherein in a non-woven fabric layer or layers, e.g., viscose rayon bonded with polyvinyl alcohol is associated with a plastic, e.g., polyethylene film. Usually, a flexible support is employed. However, it is within the purview of this invention to employ rigid supports, for example in the case of fiber and/ or particle board, wall board, dry wall, conventional acoustical ceiling material, etc.

Prior to deposition of the large capsule-containing thixotropic matrix upon the support, the support can be treated to impart patterned depressions in the upper surface therof, viz, the surface which is to receive the matrix. This can be done conveniently by embossing valleys in any desired configuration corresponding to the configuration of the embossing roll. This permits concentration of the encapsulated material in such embossed regions to tailormake articles wherein regional concentrations of the capsule components are required. For example, the capsulecontaining thixotropic matrix can be extruded onto a paper or other support having embossed depressions followed by scraping to remove excess matrix. In such an article, the capsule components will be concentrated in the desired regions.

The thickness of the supporting substrate can range from about 15 microns to about 25,000 microns. Usually, the supporting substrate thickness ranges from about microns to about 1,000 microns and, more usually, from about 200 microns to about 1,000 microns. In general, the selection of the specific support material to be employed will depend upon the specific use to which the articles are subjected in that the support provides the added strength to the binder matrix which is requisite for a given utility.

THIXOTROPIC MATRIX COMPOSITIONS As noted above, the thixotropic matrix contains a gelformer hydrophilic Water-soluble or readily water-dispersible organic polymer which has the ability to assume a swollen condition in water. It also contains a binder and other optional components, such as coloring agents, abrasives, etc., as discussed hereinbelow. The following table indicates the permissible, usual and more usual typical components.

TAB LE Thixotropie matrix Concentration (weight percent) The use of a thixotropic large capsule-containing gel matrix having the below noted viscosity characteristics prevents rapid and premature water absorption into the supporting substrate thereby maintaining the compositional integrity of the matrix uniformly thus promoting even distribution of all components. In addition, the retention of Water-soluble components of the deposited capsule-containing matrix assists in promoting the desired hand or feel of the supporting substrate.

Upon drying, according to a preferred embodiment of this invention, the capsule-containing thixotropic matrix contains (ex adjuvant fillers and capsules) a minor amount of the hydrophilic polymeric gel and a major amount of a flexible polymeric binder. Of course, usually the capsules dominate the dried matrix composition on a weight basis.

POLYMERIC GEL FORMER This gel-former is the single ingredient of the matrix most responsible for providing the requisite viscosity or thixotropic condition which enables the capsules to be deposited upon the substrate support in an eflicient manner While minimizing breakage of the large capsule cell walls. While it is preferable, in accordance with the procedural aspects of this invention to deposit the capsule-containing thixotropic matrix by extrusion; the use of a thixotropic matrix appears to provide a cushion for the capsules thereby permitting other coating procedures to be employed, and satisfactory specimens have been produced by troweling the capsule matrix onto a flexible support with spatulas and similar delivery devices.

In accordance with this invention, the viscosity of the thixotropic capsule-containing matrix compositions at the time of deposition onto the substrate (support) ranges from about 500 to about 50,000 centipoises (Brookfield) at C., usually ranges from about 1,000 to about 10,000 centipoises and more usually from about 2,000 to about 10,000 centipoises.

Suitable hydrophilic water-soluble or readily waterdispersible organic polymers which can be employed as a gel former include but are not limited to the following: methyl cellulose, carboxy methyl cellulose, carboxyethyl cellulose, various starches including natural and oxidized starches, pectin and other carbohydrate derivatives, casein and other animal derived proteinaceous polymers, wood cellulose derivatives, both cationic and anionic polyacrylamides (e.g., the commercially available Polyhall 295 marketed by the Stein Hall Co.), natural gums, e.g., karaya gum, gelatin partially hardened by aldehydic cross-linking agents to the extent whereby gel formation is not readily reversible by contact with warm water, vis, at temperatures of approximately 25 C. to 40 C.

FLEXIBLE BINDER The use of a flexible binder in the thixotropic matrix imparts several desirable properties to the matrix and to the capsule-containing articles. For example, the use of a flexible binder components(s) enhances the matrix feel or hand and assists in avoiding a harsh texture. Also, a flexible binder assists in avoiding fissures or cracks which could result in premature capsule cell wall rupture and release of internal phase contents upon extended storage. Also, many of the capsule articles are designed for repeated usage with only a portion of the encapsulated components being dispensed in each usage. In such articles,

it is important that said matrix does not prematurely release an unduly large concentration of the total capsule contents or cause dislocation of portions of the matrix from the support resulting in their littering the surface of the support to which the capsule contents are to be applied as would likely occur if the matrix were too rigid. Therefore, sufficient binder should be utilized, where the aforementioned problems are a factor, in the capsule articles to impart the extent of flexibility required for a given end use. This can be established readily by manually flexing the supporting substrate containing the matrix after drying thereof. Repeated tests can be conducted at varying time periods consonant with the expected shelf life prior to actual use.

Suitable candidate exemplary binder materials which can be employed in the thixotropic matrix include but are not limited to the following: water-soluble polyacrylates and methacrylates and lower alkyl-substituted acrylates and methacrylates, e.g., the readily available SR 2 marketed by the Rohm & Haas Co. This material is a water-soluble acrylic polymer resulting in soft, flexible films upon drying, which films retain the aforementioned properties and are substantially insoluble in water at room temperatures subsequent to their formation. Films formed from aqueous solutions of this acrylic polymer, per se, have a hardness (KHN) at room temperature of less than 1.0 after eighteen hours and retain the same hardness rating after being subjected to a temperature of 149 C. for 30 minutes. Other suitable binder materials include various natural and synthetic readily water-dispersible elastomeric latex materials, e.g., butadiene-styrene elastomers, butadiene-acaylonitrile elastomers.

OPTIONAL MATRIX ADJUVANT MATERIALS A wide variety of optional adjuvant materials can be included with the matrix at the time it is disposed on the substrate. Thus, coloring agents, dyes, pigments, etc. can be included. Additional agents such as Solka-Floc (a comminuted cellulosic fiber of vegetable origin), ground cork, pumice, silicon carbide (or other abrasives), reprocessed polyurethanes, sponge rubber, leather dust, etc. can be included.

LARGE CAPSULES These large capsules are produced by a variety of both chemical and mechanical encapsulated procedures known in the art, and are in effect generally spherically shaped. The capsules contain a solid or liquid internal phase and capsule cell wall material. Various capsule cell wall materials, e.g., gelatin-gum arabic hardened with glutaraldehyde or without other adjuvants such as copolymers of ethylene and maleic anhydride or phenolplast condensates, e.g., resorcinol-formaldehyde, nitrocellulose, etc. Other cell wall materials, e.g., other phenolplast condensates, such as phenol-formaldehyde; aminoplast condensates, such as urea-formaldehyde; polyvinyl alcohol; ethyl cellulose; polyvinylidene chlorides (saran); polycarbonates (Laxan); chlorinated polyolefins, e.g., chlorinated rubber (Parlon), etc. can be used. Moreover, each capsule or some of them can have a plurality of substantially concentric walls, e.g., a primary cell wall of gelatin-gum arabic with a secondary (outer) cell wall of nitrocellulose or ethyl cellulose. Furthermore, all or a portion of the capsules can have a composite cell wall, viz, one in which a plurality of wall forming components participate in cell wall formation in the manner of intimately associated components, e.g., a composite cell wall of gelatin-gum arabic and resorcinol-formaldehyde.

In the articles produced in accordance with this invention, the capsule contents can be released either by pressure, heat or can be ruptured chemically, e.g., by solvation (dissolving or degradative reaction with a given chemical). The release mechanism sought to be incorporated in the finished article will be a prevailing factor in selection of the specific cell wall material to be employed. Another factor is the very nature of the encapsulated material itself since the internal phase composition must not dissolve the cell wall. The individual capsule size (diameters) can range from about 400 to 5,000 microns and usually range from about 500 to about 2,000 microns. While the size of individual large capsules in any given product can vary over a wide range; the predominant concentration of capsules and hence the average capsule size usually ranges from about 800 to about 2,000 microns and more usually averages from 1,000 to 2,000 microns. Each capsule can contain payloads ranging from about 45 to 95 weight percent. However, usually the payload ranges from 50 to 95 weight percent and more usually from about 60 to 90 weight percent. The term payload as used herein means the concentration of internal phase (encapsulated) composition based on total capsule weight. The payload is expressed as a weight percent.

CAPSULE CONTENTS A wide variety of solid and liquid materials can be employed as internal phase materials (capsule contents). Moreover, mixtures of liquid and solids can be present in the same capsule. Suitable exemplary capsule contents include, but are not limited to, the following: dry cleaning solvents, e.g., perchloroethylene, trichloroethylene, carbon tetrachloride; mineral spirits; detergents and solutions thereof; lubricants and lubricating oils, including light lubricating oils for sporting use such as gun oil, leather oil, etc.; metal cleaners for silver, copper, etc., such as urea solutions, ammonium sulfamate solutions, ammoniacal solutions (with or without tarnish preventing agents); insect repellents, e.g., alkyl polyols (hexane diol), dialkyl phthalates (dimethyl phthalate); shoe polish, viz, a combination of a solvent (naphtha), a dye (black) and a dissolved Wax (paratfinic) or resin; furniture polish, such as a combination ofl solvent and wax and/ or silicone, with or without a coloring agent; windshield defrosting compositions containing glycerine or other glycols; paint removers and other cleaners, e.g., naphtha, trichloroethane; nail polish removers, such as alkyl acetates, e.g., butyl acetate, amyl acetate, hexyl acetate; cosmetics, e.g., lotions, creams, perfumes, colognes (and other fragrances), facial powder, rouge, deodorants, e.g., liquids and creams containing hexachlorophene.

ARTICLES The articles of manufacture containing the large capsules positioned within (and including embedded partially within) the flexible dried thixotropic matrix which is deposited on a supporting substrate represent a tidy and neat capsular applicator delivery device. The dried thixotropic matrix retains sulficient flexibility after drying to provide a cushion for the capsules and ward off premature capsule cell wall breakage due to assembling a plurality of applicators one upon another (as occurs, e.g., during storage, packaging, etc.); yet when moderate hand pressure is applied against the back of the applicator, e.g., from the barrier tfilm side of the supporting substrate, at least some of the capsules will break releasing their contents. Such applicators can be used repeatedly and the capsules not broken by the previous usage(s) retain their contents in unspoiled condition. In such applicators, the supporting substrate is usually a flexible layer(s).

GENERAL FORMING (PROCESS) CONSIDERATIONS Usually at the outset of the forming procedure, the thixotropic gel is established in a matrix reservoir by adding the gel-forming polymer to water with stirring. A separate supply source of the desired capsules is then fed, either dry, damp or more usually as an aqueous slurry characteristically containing from about 30 to 50 weight percent capsules, to the matrix reservoir and mixed therewith. Optional materials such as binders, fillers, coloring agents are also added thereto. When the matrix mix contropic matrix can be extruded on or between a variety of support surfaces. The drying is conducted at temperatures sufliciently high to insure removal of extraneous water and other volatiles within a reasonable time but below those temperatures which would cause damage to the capsules, the matrix, or the substrate.

The invention will be illustrated in great detail in the examples which follow. These example are included herein for purposes of illustration and. accordingly should not be considered to limit the invention.

EXAMPLE I One hundred weight parts of damp shoe polish capsules (45 weight parts of capsules on a dry weight basis) are added to an aqueous gel system containing 50 weight parts of an aqueous solution containing one weight percent of Polyhall 295 (polyacrylamide) gel former and 11 weight percent of SR2 binder. The capsules have individual sizes of 500 to 1,500 microns (average size of 1,000 microns), a shoe polish payload of 75 to weight percent and have gelatin-gum arabic cell walls hardened with glutaraldehyde in accordance with known capsule preparation procedures. The aforementioned mix is stirred to uniformly distribute the components therein.

After being thoroughly dispersed, the viscous capsule containing matrix is extruded to a thickness of approximately 0.125 inch (3,000 microns) directly onto a flexible, absorbent, creped paper surface (paper toweling material). The articles thus produced are dried at 80 to C. for three to four hours or, in general, for suflicient time to substantially dry the matrix and substrate, viz, dry to the touch. The articles are examined after drying and subjected to manual flexing. The capsular matrix retains its flexibility and no visible rupture ofi capsular contents is observed due to the gentle force applied during flexure.

EXAMPLE II The above procedure is repeated with the sole exception being that instead of a paper supporting substrate, a 3,000 micron thick, open cell foam, flexible polyurethane sheet is employed. This sheet has its undersurface. provided with a polyethylene barrier film. After drying, this capsular article likewise possesses substantially the same flexible characteristics as indicated hereinabove for the article of Example I.

EXAMPLE III The procedure of Example I is repeated except that during the extrusion procedure, a second layer of absorbent toweling is placed over the upper capsule-matrix surface. After drying, the resulting laminated sandwich structure possesses substantially the same flexibility characteristics as observed for the article of Example I.

What is claimed is:

1. A method for forming articles containing large capsules having sizes ranging from 500 to 5,000 microns comprising establishing a thixotropic matrix having a Brookfield viscosity at 25 C. ranging from about 500 to about 50,000 centipoises and containing: about 0.1 to about 10 weight percent of a hydrophilic polymeric gel former selected from the group consisting of animal derived proteinaceous polymers, anionic and cationic polyacrylamides, carbohydrate derivatives, natural gums, and starches; about 1 to about 15 weight percent of a polymeric flexible binder selected from the group consisting of natural and synthetic readily water-dispersible elastomeric materials, and water-soluble polyacrylates and methacrylates and lower alkyl-substituted acrylates and methacrylates; and from to 50 weight percent of said large capsules; depositing said matrix upon a supporting substrate and drying said capsule-containing matrix.

2. A method as in claim 1 which includes contacting an additional layer of support material with the upper surface of said capsule-containing matrix during deposition thereof to form a laminate containing said large capsules.

3. A method as in claim 1 wherein said matrix viscosity ranges from about 1,000 to about 10,000 centipoises.

4. A method as in claim 3 wherein said capsules range in individual size from about 500 to about 2,000 microns.

5. A method as in claim 4 wherein said capsule-containing thixotropic matrix is deposited upon said substrate by extrusion to substantially the desired thickness thereof.

6. A method as in claim 5 wherein said supporting substrate is flexible.

7. A method as in claim 6 wherein said flexible substrate is comprised of paper.

8. A method as in claim 6 wherein said flexible substrate comprises an open cell foam.

9. A method as in claim 6 wherein the concentration of the hydrophilic gel former ranges from about 0.1 to about 8 weight percent and the concentration of the polymeric flexible binder ranges from about 2 to about weight percent.

10. An aqueous-based capsule-containing thioxotropic matrix composition having a Brookfield viscosity at 25 C. of 500 to 50,000 centipoises and consisting essentially of the following components in their below listed concentrations:

Concentration Component: (weight percent) Hydrophilic polymeric gel former 0.1 to 10 Polymeric flexible binder 1 to 500 to 5,000 micron capsules 5 to 50 Adjuvant fillers 0 to Water, balance wherein said hydrophilic polymeric gel former is selected from the group consisting of animal derived proteinaceous polymers, anionic and cationic polyacrylamides, carbohydrate derivatives, natural gums, and starches; and said polymeric flexible binder is selected from the group consisting of natural and synthetic readily water-dispersible elastomeric materials, and water-soluble polyacrylates and methacrylates and lower alkyl-substituted acrylates and methacrylates.

11. The aqueous-based capsule-containing thixotropic composition of claim 10 having a Brookfield viscosity at 25 C. of 1,000 to 10,000 centipoises and consisting essentially of the following components in their below listed concentrations:

Concentration Component: (weight percent) Hydrophilic polymeric gel former 0.1-8 Polymeric flexible binder 115 500 to 2,000 micron capsules 1040 Adjuvant fillers 020 Water, balance, said composition being readily extrudable.

12. The aqueous-based capsule-containing thioxotropic composition of claim 11 having a Brookfield viscosity at 25 C. of from 2,000 to 10,000 centipoises and consisting essentially of the following components in their below listed concentrations:

Concentration Component: (Weight percent) Hydrophilic polymeric gel former 0.1-5 Polymeric flexible binder 2-15 500 to 2,000 micron capsules 20-40 Adjuvant fillers 0-10 Water, balance composition being readily extrudable 13. An article consisting essentially of a supporting substrate having on the upper surface thereof a flexible matrix containing a profusion of large capsules having individual sizes ranging from 500 to 5,000 microns; said matrix consisting essentially of a hydrophilic polymeric gel and a polymeric flexible binder wherein said hydrophilic polymeric gel is selected from the group consisting of animal derived proteinaceous polymers, anionic and cationic polyacrylamides, carbohydrate derivatives, natural gums, and starches; and said polymeric flexible binder is selected from thegroup consisting of natural and synthetic readily water-dispersible elastomeric materials, and water-soluble polyacrylates and methacrylates and lower alkyl-substituted acrylates and methacrylates.

14. An article as in claim 13 wherein said article includes an additional (upper) layer of substrate material adhered to the upper surface of said matrix.

15. A capsular applicator consisting essentially of a flexible supporting substrate having on the upper surface thereof a flexible matrix containing a profusion of large capsules having individual sizes ranging from about 500 to about 2,000 microns; said matrix consisting essentially of a minor abount of a hydrophilic gel and a major amount of a polymeric flexible binder wherein said hydrophilic polymeric gel is selected from the group consisting of animal derived proteinaceous polymers, anionic and cationic polyacrylamides, carbohydrate derivatives, natural gums, and starches; and said polymeric flexible binder is selected from the group consisting of natural and synthetic readily water-dispersible elastomeric materials, and water-soluble polyacrylates and methacrylates and lower alkyl-substituted acrylates and methacrylates.

16. A capsular applicator as in claim 15 wherein said flexible substrate consists essentially of paper.

17. A capsular applicator as in claim 15 wherein said flexible substrate consists essentially of an open cell foam.

18. A capsular applicator as in claim 15 which includes an additional layer of flexible substrate material in contact with the upper surface of said matrix.

19. A capsular applicator as in claim 18 wherein said additional layer is of a material different from that of said supporting substrate.

References Cited UNITED STATES PATENTS 1,752,765 4/1930 Van Sant l5209 2,980,941 4/1961 Miller 252-316 X 3,016,308 1/1962 Macaulay 252316 X 3,133,309 5/1964 Miles 117112 3,257,267 6/1966 Hay 252316 X 3,384,536 5/1968 Sandberg et al. 252-316 X RICHARD D. LOVERING, Primary Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 619 842 Dated November 16, 197 1 lnv t fls) Theodore Maierson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 15, line 6, "abount" should be amount-, and hydrophilic gel" should be hydrophilic polymeric ge1-.

Signed and sealed this 11th day of April 1972.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GO ITSCHALK Attesting Officer Commissioner of Patents 

